JP6220884B2 - Carbide coextrusion shrink film - Google Patents

Description

  The present invention generally relates to multilayer films comprising four or more separate layers. The film contains two outer layers, an internal stiffening layer, and an internal shrink layer. The outer layer includes a linear low density polyethylene resin, the stiffening layer includes polypropylene or high density polyethylene, and the shrink layer includes low density polyethylene. The multilayer film of the present invention is characterized by having a gloss of at least 62% at 45 degrees, combined with a 2% secant tensile modulus exceeding 400 MPa.

  Currently, the highest performance shrink films used for demanding collation applications are manufactured by the blown film process and typically include three layers. The two skin layers are usually based on a blend of LLDPE (often mLLDPE) with most LDPE. The central layer typically contains fractionated molten MI LDPE that is sometimes blended with HDPE. There is a growing demand for more elastic films that allow down gauge to 35 microns or less of typical 45 micron collation shrink films today. Such significant modulus increase cannot be addressed by known formulations in combination with existing formulations and existing three-layer coex technology. While the processor currently attempts to increase the modulus of elasticity by increasing the content of hard resin (mainly HDPE and sometimes PP), it minimizes resin usage and adversely affects other properties. There are limitations to this approach from the perspective of bringing about.

  However, it has been found that five-layer machines that are more prevalent in the industry in combination with innovative film formulations can be used to achieve films that meet these sustainability goals. Thus, one aspect of the present invention is a multilayer film that can be down gauged to 40 microns or less, but still have good stiffness and suitable shrink properties.

Accordingly, the first aspect of the present invention is a multilayer film comprising four or more separate layers. The film includes first and second outer layers, at least one stiffening layer, and at least one shrink layer. Each outer layer is independently characterized by a melt index in the range of 0.3-4 g / 10 min, a density in the range of 0.917-0.950 g / cm ³ , and a polydispersity of 3-9. And 60 to 100% by weight of the outer layer of a linear low density polyethylene resin.

The required stiffening layer is 1) polypropylene resin, which has a homopolymer polypropylene and more than 90% propylene and up to 10% ethylene or 4-10 carbon atoms A polypropylene resin selected from the group consisting of propylene random copolymers obtained from one or more α-olefins, wherein the polypropylene resin has a melt flow rate in the range of 0.1 to 1 g / 10 min; High density polyethylene resin, characterized by having a melt index in the range of 0.25 to 4 g / 10 min, and a density in the range of 0.935 to 0.975 g / cm ³ , and 3) from these blends 60 to 100% by weight of the stiffening layer selected from the group comprising a cured resin

The required shrink layer has a melt index in the range of 0.2 to 1 g / 10 min and a density in the range of 0.917 to 0.935 g / cm ³ . 50-100% by weight of high pressure low density polyethylene resin.

  The film of this aspect of the invention is characterized by having a gloss of at least 62% at 45 degrees in combination with a 2% secant tensile modulus greater than 400 MPa in the machine direction, the cross direction, or both the machine and cross directions It can be. Preferably, such a film has a total thickness of 40 microns or less.

Definitions and Test Methods As used herein, the term “polymer” refers to a polymeric compound prepared by polymerizing monomers, whether of the same or different types. Thus, the generic term polymer includes the term “homopolymer” commonly employed to refer to polymers prepared from only one type of monomer, as well as “copolymers” referring to polymers prepared from two or more different monomers. To do.

  “Polyethylene” shall mean a polymer obtained from ethylene monomers containing more than 50% by weight of units. This includes polyethylene homopolymers or copolymers (meaning units derived from two or more comonomers). Common forms of polyethylene known in the art include low density polyethylene (LDPE) as well as linear polyethylene. Linear polyethylene includes: linear low density polyethylene (LLDPE); very low density polyethylene (ULDPE); very low density polyethylene (VLDPE); both linear and substantially linear low density resins. Single site catalyzed linear low density polyethylene (m-LLDPE); as well as high density polyethylene (HDPE). These polyethylene materials are generally known in the art. However, the following description can help to understand the differences between some of these different polyethylene resins.

  The term “LDPE” may also be referred to as “high pressure ethylene polymer” or “highly branched polyethylene” where the polymer exceeds 14,500 psi (100 MPa) using a free radical initiator such as a peroxide. Defined to mean partially or fully homopolymerized or copolymerized in an autoclave or tubular reactor at pressure (eg, US Pat. No. 4,599, incorporated herein by reference). , 392). LDPE resins typically have a density in the range of 0.916 to 0.940 g / cm3.

  The term “LLDPE” includes both resins made using conventional Ziegler-Natta catalyst systems as well as single site catalysts such as metallocenes (sometimes referred to as “m-LLDPE”). LLDPE contains chain branches that are not as long as LDPE, and is described in US Pat. No. 5,272,236, US Pat. No. 5,278,272, US Pat. No. 5,582,923, and US Pat. No. 5,733. 155, a substantially linear ethylene polymer; a homogeneously branched linear ethylene polymer composition as in US Pat. No. 3,645,992; US Pat. No. 4,076,698. Heterogeneously branched ethylene polymers as prepared in accordance with the process disclosed in US Pat. No. 3,989; and / or blends thereof (as disclosed in US Pat. No. 3,914,342 or US Pat. No. 5,854,045). Including. Linear PE can be made via gas phase, liquid phase, or slurry polymerization, or any combination thereof, using any type of reactor or reactor configuration known in the art, Most preferred are gas phase and liquid phase reactors.

  The term “HDPE” refers to polyethylene having a density greater than about 0.940 g / cm 3, generally prepared with a Ziegler-Natta catalyst, a chromium catalyst, or even a metallocene catalyst.

  "Polypropylene" shall mean a polymer obtained from propylene monomers containing more than 50% by weight units.

  “Multimodal” means a resin composition that may be characterized as having at least two separate peaks in a GPC chromatogram showing molecular weight distribution. Multimodal includes resins having two peaks, as well as resins having three or more peaks.

  The following analysis methods are used in the present invention.

  Density is determined according to ASTM D792.

The “melt index”, also referred to as “I ₂ ”, is determined according to ASTM D1238 (190 ° C., 2.16 kg). Melt index is generally used for polyethylene-based polymers.

  “Melt flow rate”, also referred to as “MFR”, is determined according to ASTM D1238 (230 ° C., 2.16 kg). Melt flow rate is generally used for polypropylene-based polymers.

The term “polydispersity” is the same as molecular weight distribution or “MWD” and is defined as the ratio of weight average molecular weight: number average molecular weight (Mw / Mn). M _w and M _n are determined according to methods known in the art using conventional gel permeation chromatography (GPC).

  Total (overall) haze and internal internal haze: Internal haze and total haze are measured according to ASTM D1003-07.

  The 45 ° gloss is determined according to ASTM D2457-08 (average of 5 film samples).

  The 2% secant modulus -MD (longitudinal direction) and CD (transverse direction) are determined according to ISO 527-3 (average of 5 film samples in each direction).

  Shrinkage is determined in the longitudinal and lateral directions according to ISO 11501.

  Puncture resistance is determined according to ASTM D-5748.

Film The film of the present invention is a multilayer film comprising 4 or more separate layers. The film includes first and second outer layers, at least one stiffening layer, and at least one shrink layer. The film preferably has a total thickness of 40 microns or less, preferably 35 microns or less. Although there is no possible minimum thickness for the film of the present invention, current manufacturing equipment implementation considerations suggest that the minimum thickness is at least 8 microns.

  It should be understood that while the film must have a minimum of 4 layers, it may have more than 4 layers. Specifically, the film structure of the present invention may include an additional stiffening layer, an additional shrinking layer, or an additional layer that is neither a shrinking layer nor a stiffening layer. Such additional layers may provide different functionalities such as, for example, barrier layers or tie layers as are generally known in the art. One preferred embodiment is a five-layer film having an outer layer, a stiffening layer, a shrink layer, a second stiffening layer, and a second permanent layer.

  The film of this aspect of the invention is at least 60% at 45 degrees combined with a 2% secant tensile modulus of greater than 400 MPa, preferably at least 450 MPa, in the machine direction, or in the machine direction, or in both the machine and transverse directions. , Preferably having a gloss of at least 65%. The film of the present invention preferably has a total haze of less than 10%.

  The films of the present invention preferably have an average shrinkage in the machine direction of 40-90%, preferably 50-70%, and an average shrinkage in the transverse direction of 0-25%, preferably 5-20%.

The films of the present invention also preferably have a puncture resistance of at least 2 J / cm ³ , more preferably at least ³ J / cm ³ .

  The films of the present invention can be advantageously used for any purpose generally known in the art. Such uses include transparent shrink films, collation shrink films, shrink footer films, heavy transport bags, block bottom bags and stand-up pouch films, liner films, longitudinally oriented films, and diaper compression packaging bags. But is not limited to these. Different methods may be employed to produce such films. Suitable conversion techniques include, but are not limited to, blown film processes, cast film processes, vertical or horizontal foam fill sealing processes. Such techniques are generally well known. In one embodiment, the conversion technique includes but is not limited to an inflation film process.

Each outer layer of the outer layer film is independently 0.3 to 4 g / 10 min, preferably a melt index in the range of 1 to 2 g / 10 min, and 0.915 g / cm ^{3 to} 0.950 g / cm ³ , preferably 60-100 wt% linear low density polyethylene (LLDPE) of the outer layer, characterized by having a density in the range of 0.919 to 0.935 and an MWD of 3-9, preferably 3.2-4 ) Contains resin. The LLDPE is preferably produced using Ziegler-Natta catalyst technology as is generally known in the art.

Optionally, the outer layer (s) of the film of the present invention also has a melt index in the range of 0.25 g / 10 min to 4 g / 10 min, preferably 0.3-1 g / 10 min, and 0.918-0. 0 to 40% (by weight of outer layer) of the first high pressure low density polyethylene resin characterized by having a density in the range of .935 g / cm ³ , preferably 0.923 to 0.928 g / cm ^3. May be included.

  Although not essential, it may be preferred for many applications that the same resin composition be used in each of the outer layers.

  Each outer layer preferably constitutes 5 to 25%, preferably 8 to 12.5% of the total thickness of the film.

Stiffening layer (including multiple layers)
The required stiffening layer comprises 60-100% (by weight of stiffening layer) of cured resin. For the purposes of the present invention, “cured resin” is defined as being one selected from the group consisting of polypropylene resin, high density polyethylene (HDPE) resin, or blends thereof. The polypropylene resin may be a homopolymer polypropylene (“hPP”) or a propylene random copolymer (“RCP”). When RCP is used, it is preferred that the comonomer is obtained from more than 90% by weight of propylene units. The remaining portion of RCP (ie, up to 10% by weight) is derived from ethylene or one or more alpha olefins having 4 to 10 carbon atoms. Regardless of whether hPP or RCP, or blends thereof are used, the polypropylene resin may have a melt flow rate in the range of 0.1-2 g / 10 min, preferably 0.5-1.5 g / 10 min. preferable.

When HDPE resin is used, it has a melt index in the range of 0.1 g / 10 min to 4 g / 10 min, preferably 0.25 to 2 g / 10 min, and 0.935 to 0.975 g / cm ³ , Preferably it has a density in the range of 0.945 to 0.965 g / cm ³ . It is also contemplated that each stiffening layer may include a different HDPE blend.

  The stiffening layer may comprise a single polymer as described above or may be a blend of two or more of these polymers. In addition, it is contemplated that any stiffening layer may also comprise up to 40% (by weight of stiffening layer) of a non-cured polymer or polymer blend, although for many embodiments, It is preferable that 100% of the resin used in the stiffening layer is a cured resin.

  Regardless of whether it is a single layer or multiple layers, it is preferred that the stiffening layer comprises 20-70%, preferably 35-50% by weight of the total film structure. For some applications, it may be preferred that the film comprises at least 40% by weight of the film structure.

  In a preferred five-layer structure with two stiffening layers, for many applications it is preferred that each stiffening layer consists of the same resin formulation.

Shrink layer (including multiple)
The required shrinkage layer has a melt index in the range of 0.2-1 g / 10, preferably 0.3-0.6 minutes, and 0.917-0.935 g / cm ³ , preferably 0.925-0. 50% to 100% (by weight of shrink layer) high pressure low density polyethylene resin characterized by having a density in the range of 928 g / cm ³ . This second LDPE may be the same as or different from any first LDPE described for use in the outer layer. For many applications, it may be preferred that the resin used for the shrink layer comprises 100% high pressure low density polyethylene resin.

For some applications, the shrink layer further has a melt index in the range of 0.2 g / 10 min to 4 g / 10 min, preferably 0.5 to 1 g / 10 min, and 0.930 to 0.975 g / cm ^3. It may be preferred to contain 0-50% of a second linear high density polyethylene resin, characterized in that it preferably has a density in the range of 0.935 to 0.965 g / cm ³ . This second linear high density polyethylene resin may be the same as or different from any first linear high density polyethylene resin described for the stiffening layer. The addition of linear high density polyethylene resin to the shrink layer may be preferred especially when it is desirable to impart additional deformation resistance to the film.

  Regardless of whether as a single layer or multiple layers, the shrink layer preferably comprises 30-70%, preferably 35-50% of the total thickness of the film.

  The following resins were used to make films to demonstrate the effectiveness of the present invention.

Resin A is an LLDPE having a density of 0.935 g / cm ³ , a melt index of 1.7 g / 10 min, and an MWD of 3.4.

Resin B is an LLDPE having a density of 0.935 g / cm ³ , a melt index of 0.5 g / 10 min, and an MWD of 3.1.

Resin C is a high pressure low density polyethylene resin having a density of 0.925 g / cm ³ and a melt index of 1 g / 10 min.

Resin D is a linear high density polyethylene resin having a density of 0.960 g / cm ³ and a melt index of 0.29 g / min.

Resin E is a linear high density polyethylene resin having a density of 0.956 g / cm ³ and a melt index of 2 g / min.

Resin F is a linear high density polyethylene resin having a density of 0.955 g / cm ³ and a melt index of 4 g / min.

Resin G is a high pressure low density polyethylene resin having a density of 0.926 g / cm ³ and a melt index of 0.3 g / 10 min.

  The resin is used to make a coextruded film of A / B / C / B / A (or A / B / A structure for the comparative example) using the resin components shown in the table below. The

  In each case, the total film thickness was 35 microns and the breakdown between layers was 10% / 20% / 40% / 20% / 10%. The film is evaluated for 2% secant modulus, 45 ° gloss, haze, shrinkage, and puncture resistance. The results are included in the following table.

Claims (17)

A multilayer film comprising four or more separate layers,
a. First and second outer layers, each outer layer being independently
i. 60-100 weight of said outer layer, characterized by having a melt index in the range of 0.3-4 g / 10 min, a density in the range of 0.917-0.950 g / cm ³ , and an MWD of 3-9. % Linear low density polyethylene resin,
ii. A first high pressure of 0 to 40% by weight of the outer layer, characterized by having a melt index in the range of 0.3 to 4 g / 10 min and a density in the range of 0.918 to 0.935 g / cm ^3. Low density polyethylene resin,
First and second outer layers comprising:
b. At least one internal stiffening layer, wherein the stiffening layer (s) cumulatively comprises at least 20% by weight of the film, each stiffening layer being independently
i. 1) Polypropylene resin, wherein the polypropylene resin is derived from homopolymer polypropylene and more than 90 wt% propylene and up to 10 wt% ethylene or one or more alpha olefins having 4 to 10 carbon atoms Selected from the group consisting of propylene random copolymers, wherein the polypropylene resin has a melt flow rate in the range of 0.1-2 g / 10 min, and 2) 0.25-4 g / From a first linear high density polyethylene resin characterized by having a melt index in the range of 10 minutes and a density in the range of 0.935 to 0.975 g / cm ³ and 3) these blends An internal stiffening layer comprising 60-100% by weight of a cured resin selected from the group consisting of: ,
c. At least one internal shrink layer, each shrink layer independently
i. 50-100% by weight of the second shrink layer, characterized by having a melt index in the range of 0.2-1 g / 10 min and a density in the range of 0.917-0.935 g / cm ³ . High pressure low density polyethylene resin,
ii. Second linear high density of 0-50%, characterized by having a melt index in the range of 0.2-4 g / 10 min and a density in the range of 0.930-0.975 g / cm ³ Polyethylene resin,
Including an inner shrink layer,
Including
The multilayer film has a gloss of at least 60% at 45 degrees, combined with a 2% secant tensile modulus greater than 400 MPa in the machine direction, the cross direction, or both the machine direction and the cross direction. ,
Multilayer film.   The multilayer film of claim 1, wherein the film comprises at least five layers, two of which are stiffening layers.   The multilayer film of claim 2, wherein each outer layer comprises the same material and each stiffening layer comprises the same material.   The multilayer film according to claim 1, wherein the first high-pressure low-density polyethylene resin and the second high-pressure low-density polyethylene resin are the same.   The multilayer film according to claim 1, wherein the first high-pressure low-density polyethylene resin in the outer layer has a melt index in the range of 0.8 to 1.5 g / 10 minutes. The multilayer film according to claim 1, wherein the high-pressure low-density polyethylene resin in the outer layer has a density of 0.923 to 0.928 g / cm ³ .   The multilayer film according to claim 1, wherein the resin used in each internal stiffening layer includes only the cured resin.   The multilayer film of claim 1, wherein the polypropylene has a melt flow rate in the range of 0.5 to 1.5 g / 10 minutes.   The multilayer resin according to claim 1, wherein the resin used in each internal shrinkage layer includes only the second high-pressure low-density polyethylene.   The multilayer film of claim 1, wherein the multilayer film has a total thickness of 35 microns or less.   The multilayer film of claim 1, wherein each outer layer comprises 5-25% of the total thickness of the film.   The multilayer film of claim 1, wherein the stiffening layer (s) constitute 20-60% of the total thickness of the film in total.   The multilayer film of claim 1, wherein the shrink layer (s) constitute 30-70% of the total thickness of the film in total.   The multilayer film of claim 1, further having a total haze of less than 10%.   The multilayer film according to claim 1, further having an average shrinkage in the longitudinal direction of 40 to 90%.   The multilayer film according to claim 1, further having an average shrinkage in the transverse direction of 0 to 25%. The multilayer film according to claim 1, further having a puncture resistance of at least 2 J / cm ³ .